1. Field of the Invention
This invention relates to a magnetic recording medium and more particularly, it is concerned with a magnetic recording medium having well-balanced excellent properties as to video head abrasion, still life, video S/N, drop out, etc.
2. Description of the Prior Art
In a magnetic recording medium comprising a non-magnetic support and a magnetic recording layer coated thereon consisting of a ferromagnetic powder and a binder, for example, video tapes, audio tapes, memory tapes, etc., it has eagerly been desired lately to improve the properties thereof and in the case of small-sized video tape recorders, in particular, severer conditions are required. Even if the pointed end width of a video head becomes 10 microns in future, a tape is contacted with the video head at a relative speed of 3 to 7 m/sec (about 20 km/hr) and in that case, it is also required to hold the abrasion of the video head in 10 .mu./300 hrs or less and the still frame life in 90 minutes or longer. 100 hours of head abrasion extends to a whole length of 2000 km and the still life is also regarded as expired when the surface of a video head is contaminated in a thickness of 0.1 micron or more.
Up to the present time, various magnetic compositions have been proposed such as using an abrasive agent having an Mohs' hardness of at least 6 and monobasic fatty acid described in Japanese Patent Publication No. 39402/1974 and containing a non-magnetic powder having a Mohs' hardness of at least 9 and granular .alpha.-F.sub.2 O.sub.3 powder described in Japanese Patent Application (OPI) No. 129955/1980. However, these compositions cannot satisfy all the properties such as still life, head abrasion, drop out, video S/N, etc.